The trial of a Chicago businessman accused of helping plan deadly attacks in Mumbai in 2008 is being closely watched worldwide for what testimony might reveal about the global fight against terrorism. Defense attorneys, though, say their case is about just one thing: Betrayal.

Opening statements start Monday in the trial of Tahawwur Rana, who prosecutors allege provided cover for his former schoolmate to scout out sites for the rampage that killed more than 160 people in India's largest city. Rana, 50, has pleaded not guilty.

The case has drawn keen interest because the testimony might give clues about suspected links between the Pakistani militant group blamed in the attacks and the nation's main intelligence agency, which has been under scrutiny for failing to detect Osama bin Laden since U.S. forces killed him May 2 outside Islamabad.

Prosecutors' key witness is expected to be David Coleman Headley, a Pakistani-American and Rana's former friend who pleaded guilty last year to laying the groundwork for the Mumbai siege blamed on the militant group Lashkar-e-Taiba. Headley is cooperating with the government and may discuss allegations that Pakistan's government knew — or possibly helped plan — the attack. Six Americans were among those killed.